The changeover from so-called CRT televisions to liquid crystal displays is remarkable together with a display revolution in recent years. Concerning liquid crystal displays, the process of working and implementing an optical sheet for a certain essential component such as a polarizing plate includes applying a pressure-sensitive adhesive or the like to a transparent protective film for surface protection, such as a polyethylene film, a polypropylene film, or a polyester film (namely, a so-called surface protective film), for the purpose of bonding it to the component, and laminating them before use. After the laminate is incorporated into a liquid crystal display or the like, the protective film is peeled and removed. At the time of peeling, however, a so-called “separation electrification” phenomenon can occur, and thus there is a problem in which dust can be deposited due to the static electricity, or the attached component itself can be charged to catch dust. For example, the problem of the dust deposition is also a serious problem with a manufacturing process, because it is difficult to determine, at the time of product inspection, whether the problem is caused by a defect in a liquid crystal component itself or by the dust deposited on the surface and because inspection cannot be smoothly performed. In recent years, particularly high-definition displays suffer from not only the problem by dust deposition but also the problem of the breakdown of an electronic display element by separation electrification.
On the other hand, antistatic agent-blended polyethylene or polypropylene films have low transparency so that there is a problem in which the low transparency of the protective film can reduce inspection accuracy or make inspection slow when products are examined for defects after liquid crystal displays or the like are assembled.
Even in cases where highly transparent polyester films are used, untreated products have no antistatic properties and thus frequently cause troubles due to electrification, such as dust deposition. In order to solve the problem, antistatic agent-blended polyester films or antistatic agent-coated polyester films are investigated. For example, it is proposed that an ion-conductive antistatic agent should be used in combination with an acrylic resin or the like so that an antistatic layer with good transparency can be formed even when an in-line coating process is used, which includes coating, drying, stretching, and heat-treating in a film-forming process (Japanese Patent Application Laid-Open (JP-A) No. 61-204240).
Examples of the proposed products using electron-conductive antistatic agents include polyaniline-based antistatic agents (JP-A No. 07-330901), tin oxide-based anti-static agents (JP-A No. 07-329250), and polythiophene-based antistatic agents (JP-A No. 01-313521). Specifically, it is also proposed that a coating liquid containing en electron-conductive polythiophene-based antistatic agent and a latex polymer should be applied (JP-A No. 06-295016).
In the above-mentioned lamination process using a pressure-sensitive adhesive, an accidental deposition of the pressure-sensitive adhesive, particularly a deposition on the other surface of the laminated film, should be easily wiped off. Namely, so-called anti-fouling properties are required for the same reason as mentioned above, and the formation of a layer having antifouling properties, and the like are proposed (JP-A No. 2003-154616).
Next, a description is given of transfer foils.
Transfer foils are generally used in a process including the steps of laminating the subject to be transferred on the surface of the transfer foil used as a base material and transferring the subject to the desired product or the like as needed. Recently, with environmental awareness growing in these days, a new look has been taken particularly at such a process, for the purpose of forming figures or patterns with no organic solvent in the final process of manufacturing products, or the like.
For example, plastic or metallic products for use in home electric appliances, car components, house building materials, graphic products, security products, safety display-related products, and the like have been diversified in design, so that products whose surfaces have precision figures or patterns incomparable with conventional ones have been used. An in-mold transfer process, a vacuum press transfer process, a hot stamping foil process, and the like are used to print patterns on such plastic or metallic products. For example, the in-mold transfer process includes the steps of previously placing a transfer foil at a certain position in a die or mold and then press-injecting a resin into the mold from an injection molding machine so that molding and patterning from the transfer foil are performed at the same time. The vacuum press transfer process includes the steps of placing a transfer foil opposite to a molded product, reducing the air pressure between the transfer foil and the molded product such that the transfer foil comes into contact with the molded product surface, and pressing and heating them to form patterns from the transfer foil.
The market for Information Technology, flat panel displays, cellular phones, optical applications, and the like has been rapidly expanded. Under the circumstances, not only the conventional pattern transfer process, but also the process of imparting anti-scratch resistance by applying an organic solvent-containing hard-coating paint and UV-curing it, which is conventionally used when a final product is assembled, or the process of forming a hard coat layer and an adhesive layer on the transfer foil and using the laminate for transfer in product assembling, which is performed in a manufacturing process with waste disposal facilities, have been used in optical applications of very high quality, which has never been expected.
Thermoplastic resin films are preferably used as base films for these transfer foils. Particularly in terms of heat resistance and formability, polyester films are preferably used. In the basic structure of the transfer foil, a release layer, a pattern layer and an adhesive layer are formed in this order on one side of a polyester base film. The pattern layer may be formed on the whole surface or part of the surface.
There is disclosed a film for transfer foils, which includes a polyester film and a polyester resin-based coating formed on at least one side of the polyester film. However, this is for the purpose of improving the adhesion between the polyester base film and a release layer (JP-A No. 10-114039).
On the other hand, with an increase in manufacturing process speed, a discharge phenomenon or a spark is caused by separation electrification in an unwinding process, or with an increase in pattern precision, deposition of dust has been considered as an extremely undesirable matter. Thus, antistatic properties are required of transfer foils, and in recent years, the demand for such a function has become stronger, so that antistatic properties at low humidity or a conductivity level corresponding to 106 Ω/□ or less can be required. For imparting antistatic properties, for example, there are disclosed a method of forming a coating of a polyester resin to which a low-molecular weight antistatic agent is added (JP-A No. 60-141525), a method of forming a coating of an antimony-doped tin oxide conductive agent which is a humidity-independent, electron-conductive-type antistatic agent (JP-A No. 07-329250), and a method of forming a coating of a polythiophene-based conductive agent which is an electron-conductive-type antistatic agent (JP-A No. 09-31222).
The above conventional techniques, however, have the problems as described below.
The above conventional techniques for imparting antistatic properties have problems in which when ion-conductive-type antistatic agents are used, their conducting mechanism depends on adsorption of water from the air by ions and thus they are necessarily humidity-dependent (in particular, the low-molecular weight type used is significantly humidity-dependent), so that no electrical conductivity can be produced in a low-humidity environment such as a winter season.
When electron conductive agents such as antimony-doped tin oxide-based anti-static agents and polythiophene-based antistatic agents are used in which conjugated electrons are used for the conducting mechanism, the humidity dependency as described above is absent, but the composition itself is rigid and thus has no stretch following capability, for example, when an in-line coating process is used in which coating, drying, stretching, and heat treatment are preformed in a film-forming process, so that a problem can occur in which the coating film can be cracked or whitened by stretching and can cause troubles at the time of the product inspection as mentioned above.
Only the antistatic agent coating technique cannot provide antifouling properties or releasability for the antistatic layer. As mentioned above, therefore, for example with respect to polarizing plate-protective films and the like, it is difficult to determine at the time of product inspection whether the trouble is caused by a defect in a liquid crystal component itself or by surface deposition of a pressure-sensitive adhesive, so that a serious problem with the manufacturing process, such as inhibition of smooth inspection, can occur.
The case where a film with a rough surface or a film having coarse projections is used also has a similar problem in which it is difficult to determine whether the defect-like matter is caused by a defect in a liquid crystal component itself or simply by a defect in the film, such as a projection-derived defect.
The transfer foil or the like can also cause a serious problem in which the surface of the polyester base film opposite to the pattern or adhesive layer side is blocked with the adhesive layer so that the film cannot be unwound from a roll. Thus, a so-called “release function layer” is necessary on the opposite side of the polyester base film to prevent the blocking event with the adhesive layer, which has become highly and strongly adhesive in recent years. However, products satisfying such requirements have not yet been obtained.
In applications for which the market has been rapidly expanded, such as Information Technology, flat panel display, cellular phone, and optics applications, the smoothness or glossiness of the surface of a component is very important after peeling, for example, in a case where an optical film used as a component of a laminate, a protective film therefore or the like is peeled from a transfer film before use. However, products satisfying anti-static properties and smoothness at high level have not yet been obtained.